1. Field of the Invention
The present invention relates to a vertical nitride light emitting device, and more particularly, to a luminescent nitride semiconductor light emitting device greatly improved in current spreading effects.
2. Description of the Related Art
In general, a group III-V semiconductor light emitting device is made of a semiconductor material having a composition expressed by AlxInyGa(1-x-y)N, where 0≦x≦1, 0≦y≦1 and 0≦x+y≦1. The nitride semiconductor has its crystal grown on a limited type of growth substrate such as a sapphire substrate in view of lattice constant.
The sapphire substrate is electrically insulating so that the nitride semiconductor device has p- and n-electrodes formed on the same plane. But this structure disadvantageously causes current to be crowded laterally, thereby degrading current spreading effects. To overcome the problem associated with current spreading effects by a structural approach, a vertical light emitting device has been vigorously studied. Here, the vertical light emitting device has the two electrodes formed on opposed faces.
FIG. 1 illustrates an example of a conventional vertical nitride light emitting device.
As shown in FIG. 1, the nitride light emitting device 10 includes an ohmic contact layer 16, a p-type nitride semiconductor layer 14, an active layer 13 and an n-type nitride semiconductor layer 12 formed sequentially on a conductive substrate 18. On the n-type nitride semiconductor layer 12, an n-electrode 19 constructed of a transparent electrode layer 10a and an n-type bonding metal 19b is formed. Of course, a p-type bonding metal (not illustrated) may be formed underneath the conductive substrate 18.
The vertical nitride light emitting device 10 allows current to flow vertically, thereby improving current spreading effects. However, even in the vertical structure, disadvantageously current is crowded toward a central portion due to the location of the bonding metal 19b. Therefore, as shown in the light emitting device of FIG. 1, a current blocking layer 15 is additionally formed on a surface of the p-type nitride semiconductor layer in a central portion thereof, thereby spreading current uniformly across an overall area and enhancing light emitting efficiency as indicated with arrows.
The current blocking layer 15 is made of an insulating material of e.g., silicon dielectrics such as SiO2. However this insulating material for the current blocking layer 15 exhibits relatively higher light absorption coefficient, thus causing light generated from the active layer not to be extracted but to be absorbed into the current blocking layer 15 with significant loss. This potentially reduces actual light emitting efficiency.
Therefore, in the art, there has been a demand for a novel method of improving current spreading effects without light loss in the vertical nitride light emitting device.